1. Field of the Invention
The present disclosure relates generally to down-hole measurements related to oil and gas exploration and drilling operations. More particularly, embodiments of the disclosure relate to systems and methods for communicating data related the down-hole measurements from below a mud motor to destinations above the mud motor.
2. Background
Wellbores are often drilled through a geologic formation for hydrocarbon exploration and recovery operations. Measurements can be made in the wellbores related to various properties of the geologic formations, e.g., hardness, porosity, etc., and also to the properties of the wellbores themselves such as direction or inclination. Often, these measurements are made while the wellbores are being drilled. Systems for making these measurements during a drilling operation can be described as logging-while-drilling (LWD) or measurement-while-drilling (MWD) systems, and generally include various sensors carried by a bottom hole assembly (BHA) of a drill string. These measurements can be useful in steering a drilling apparatus, e.g., to maintain a predetermined path of a wellbore, and/or these measurements may be evaluated once the wellbore is complete for planning future operations.
At least some of the sensors of an LWD or MWD system may be disposed as near a down-hole end of the BHA as possible to provide measurements representative the conditions in which a drill bit is operating. Data provided by the sensors can be telemetered up-hole to a surface location or to other portions of the drill string by a telemetry tool located in the BHA. The telemetry tool may communicate with a variety of technologies including, e.g., mud pulse, electromagnetic and acoustic technologies. In some instances, a mud motor may be included in a BHA to drive the drill bit, and communication across the mud motor may be required between the sensors and the telemetry tool. A mud motor generally operates by turning a shaft in response to the passage of high pressure drilling fluid therethrough. Due in part to the rotational nature of a mud motor, transmission of information from the sensors disposed below the mud motor to a telemetry unit above the mud motor can be challenging. In some systems, a direct wired connection is passed through the mud motor to couple the sensors to the telemetry unit. The wires can be susceptible to erosion by the drilling fluid, and thus, the reliability of these systems can be limited. Other systems, such as “short-hop” electromagnetic systems, are used to communicate data across a mud motor. These systems may be adversely affected by electromagnetic properties of the geologic formation or by operation of the mud motor or other components of the BHA. Systems for transmitting data across a mud motor (in both up-hole and down-hole directions) remain lacking in the hydrocarbon drilling arts.